1. Field of the Invention
The present invention relates to a projection exposure apparatus and a device manufacturing method employing the same, which are suitable for use in a lithographic process in the device manufacturing processes for semiconductor devices, such as ICs or LSIs, imaging devices, such as CCDs, display devices, such as liquid crystal panels, and other devices such as magnetic heads.
2. Description of the Related Art
In recent years, an increase in the number of components per IC or LSI chip, forming a semiconductor device, has been increased. So far as a reduction projection exposure apparatus (stepper) for sequentially exposing a large number of areas on a photosensitive substrate by the step and repeat method by repeating formation of a circuit pattern image of a mask (reticle) on the photosensitive substrate by a projection optical system is concerned, various proposals have been made to improve resolution thereof.
Conventional examples of such resolution improving methods include a method of shortening the exposure wavelength, a method of increasing an aperture (NA) of a projection lens, a phase shifting method of improving the resolution by partially inverting the phase of a light which transmits through a cyclic pattern and a modified illumination method of improving the resolution by illuminating a cyclic pattern obliquely.
In addition, the method of improving the resolution by controlling the polarized state of light which illuminate a pattern is also known. The theoretical relation between the polarization of illuminating light which illuminate a pattern and the resolution has been described in detail in, for example, Optical Engineering, Vol. 31 (1992) p. 2657, and SPIE Vol. 1927 (1993) p. 879.
To obtain a high resolution power, for example, in a cyclic pattern 101 shown in FIG. 5 by controlling the polarized state of illumination light, linearly polarized light polarized in a direction parallel to the longitudinal direction of the respective patterns, indicated by a bidirectional arrow 102, is employed as the illumination light.
It is, however, to be noted that the use of the linearly polarized light as the illumination light for illuminating the patterns is not requisite, and the use of linearly polarized light polarized in a direction parallel to the longitudinal direction of the images of the patterns as light used to form the images of the patterns when the image of the patterns are formed is substantially essential.
The method of improving the resolution by controlling the polarized state of the illumination light falls into a method of illuminating a pattern with polarized light obtained by providing a polarizing film immediately before the pattern on a reticle and a method of providing a desired linearly polarized light obtained by rotating a polarizing plate. In the former method, if patterns 103, 104 and 105 directed in various directions, shown in FIG. 6, are available as patterns on a reticle, polarizing films 109, 110 an 111 for transmitting polarized components directed in directions indicated by bidirectional arrows 106, 107 and 108 therethrough are provided according to the patterns to improve the resolution. In the latter method, the direction of polarization of the light which has transmitted a polarizing plate 120 is restricted to a direction indicated by a bidirectional arrow 121, as shown in FIG. 7.
Generally, a reticle has thereon cyclic patterns directed in various directions, and the resolution of patterns, such as a pattern 122, whose longitudinal direction coincides with the direction of polarization can be improved because the longitudinal direction of the image of the pattern formed on an image plane is parallel to the direction of polarization.
However, regarding the patterns directed in directions other than the direction indicated by 121, an improvement in the resolution cannot be expected. Particularly, the resolution of a pattern, such as a pattern 123, whose longitudinal direction is perpendicular to the direction of polarization deteriorates when compared to that obtained when a normal non-polarized illumination light is used.